1. Field of the Invention
The present invention relates to an apparatus for reading coded symbologies on an object while determining the distance from the apparatus to the object. More particularly, it relates to a scanning device that determines the distance from the scanner to the object to allow for the focusing of the scanning beam such that high resolution, reflected light can be obtained from the object surface. Most particularly, the invention is directed to an automatic scanning system which accurately determines the distance and subsequently focuses the scanning beam onto an object for accurately reading coded symbologies.
2. Description of the Prior Art
To reduce costs and increase the volume of packages handled, the shipping industry has embraced automated package handling. This has been accomplished through package identification by coded symbologies placed on the packages and sorting performed by automated equipment using scanners that have the capability of reading the label and then routing the packages.
A scanner used in this application must be capable of reading different coded symbologies at varying distances due to different object sizes. One limiting factor in reading coded symbologies is the size of the laser spot at the label distance. Depending upon where the scanner has been prefocused, the laser spot will be larger in front of and behind the prefocused distance. The usable range where the laser spot size is acceptable is commonly referred to as the depth of field.
In an effort to increase the depth of field of a scanning system, various methods have been tried. Some methods rely upon several laser scanners prefocused for different object heights thereby having a large aggregate depth of field. Others rely upon folded light paths to increase a len's focal length or special angular solutions for the optics. Other external methods include light curtains and photoeyes to determine the height of an object which must then be input into the scanning system to electromechanically focus a lens element of the scanning beam.
In order to increase the efficiency and reduce the cost of a scanning system, it is desirable to have a low cost, lightweight compact means for providing a distance measurement internal to a scanning system to allow for the precise focusing of the scanning beam.